refactor: unify inquiry status strings using constants (P1-06)

Problem: Inquiry status values were hardcoded as strings in multiple places:
- InquiryList.razor: Status="new", Status="consulting", etc.
- InquiryDetail.razor: inquiry.Status = "consulting"
- Makes it error-prone to update status values globally

Solution:
- Add public const fields to InquiryStatusMapper for all status values
- Replace hardcoded strings with constants (StatusNew, StatusConsulting, etc.)
- InquiryList and InquiryDetail now use mapper constants

Result: Single source of truth for status values. Changing a status value now
requires only updating InquiryStatusMapper, and all usages automatically update.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/TaxBaik.Web.Client/Components/Admin/Pages/Inquiries/InquiryDetail.razor

@@ -1,6 +1,7 @@
 @page "/admin/inquiries/{InquiryId:int}"
 @rendermode @(new InteractiveWebAssemblyRenderMode(prerender: false))
 @attribute [Authorize]
+@using TaxBaik.Application.Services
 @using TaxBaik.Web.Services
 @inject IInquiryBrowserClient InquiryClient
 @inject NavigationManager Navigation
@@ -179,7 +180,7 @@ else
             if (clientId > 0)
             {
                 inquiry.ClientId = clientId;
-                inquiry.Status = "consulting";
+                inquiry.Status = InquiryStatusMapper.StatusConsulting;
                 Snackbar.Add("고객 카드가 생성되었습니다.", Severity.Success);
             }
             else